Liquid dispensing devices such as spray bottles are well known. Some offer pre-compression so as to insure a strong spray when the trigger is pulled and prevent leakage. Sprayers and foamers can be easily manufactured and filled, and are often used to dispense cleaners of all types, for example. However, in many circumstances it is preferred not to have to continually pump a dispensing device to push out the dispensed liquid. Rather, it would be much more convenient to be able to continue the spray or foam substantially past the user pulling a trigger or otherwise actuating the sprayer head. For example, if by actuating a sprayer head a certain reasonable number of times per minute a continuous spray could be obtained, many users would find that optimal.
One set of dispensing devices that provide a continuous spray are aerosol dispensers, such as are used for cooking spray (e.g. Pam®), insect spray (e.g. Raid®), lubricants (e.g. WD-40®), and a host of other uses. Aerosols hold a liquid or other dispensate under pressure such that when a user activates the device (e.g., by pressing a button) the pressurized contents are allowed to escape. However, aerosols present both significant environmental hazards as well as packaging drawbacks, which result from the necessity of using an aerosol propellant in them, and the further necessity of pressurizing them. This requires filling such devices under pressure, using packaging strong enough to withstand the pressure, and taking steps to insure that the propellant maintains a uniform pressure over the life of the can or container. Such conditions often require use of non-environmentally friendly materials and ingredients.
Additionally, conventional aerosols do not continue spraying unless the user keeps their finger on the button. Inasmuch as people generally push on the aerosol can with the index finger of their dominant hand, this requirement precludes their ability to do anything with the spray or the surface/object on which the spray is directed with that hand making it difficult to clean, etc. Thus, users are forced to spray, for example, a cleaner on a surface, then stop spraying, then wipe or scrub, etc.
Recently floor cleaning products have emerged to replace mops. Many try to spray a cleaning fluid or floor care product from one or more nozzles while a user is pushing the device along the floor or surface. Some of these devices utilize a motorized pump, run by a power cord or battery. However, such devices are often not robust, and do not last long. Or, for example, in the case of battery powered floor cleaners, any serious current draw requires large batteries, and frequent changing of same, which is both environmentally unfriendly, cumbersome and expensive.
Finally, although conventional pre-compression sprayers control the minimum output pressure, they do not in any way control the maximum output pressure. A conventional sprayer starts dispensing at a low pressure. During a trigger stroke, the pressure rises up to a peak pressure. The liquid is forced through an orifice, but only a part of the liquid can pass the nozzle, so the pressure will build up within the sprayer. Towards the end of the stroke, the liquid pressure drops to zero. The low pressure at the beginning and end of the stroke thus creates larger, non-uniform droplets at the right and left sides of the conventional sprayer pressure time curve.
A pre-compression sprayer starts spraying when the liquid pressure is at a pre-determined pressure. This pre-determined pressure is known as the “cracking pressure” of the outlet valve. As noted, during a trigger stroke the pressure rises to a peak pressure. When the pressure drops to a predetermined pressure (closing pressure of the outlet valve) dispensing stops immediately. The droplet size at the beginning and end of a dispensing stroke in a pre-compression sprayer are smaller because the pressure is higher. The peak pressure, creating even smaller droplets, is also higher than that of a conventional sprayer, because the same amount of liquid is dispensed in a shorter time. Therefore more pressure builds up. Thus, relative to a conventional sprayer the pressure difference across the pressure time curve will still be there and even be greater. It is only shifted to a higher pressure range. Thus, difficulties with standard pre-compression sprayers include, for example, (1) wider spreading droplet sizes, and (2) too small droplet sizes.
Additionally, in “direct action” type sprayers, where a user wants the spray to cease as soon as he or she stops triggering, it is desirable that the pre-compression outlet valve have a binary action, i.e. it closes effectively immediately. To achieve this, the pressure difference between opening and closing pressures of the outlet valve is optimally small. Conventionally, however, this is not the case.
In order to control outlet pressures of droplets, and to also allow for continuous spray between trigger strokes (thus imitating the operative functionality of aerosol sprayers), a buffer may be used in combination with a pre-compression valve. This results in a precise band of outlet pressures, and moves the upper portion of the pressure-time curve to the time interval between downstrokes, as described in detail in WO 2014/074654 A1 referenced above. However, when such a combination is implemented, a pre-compression valve, which sets the minimum output pressure, may require a significant opening pressure. This makes priming an issue, as to evacuate the air in the pump through the outlet valve requires sufficiently compressing it to reach the opening pressure of the outlet valve. If there are a number of interior channels, such as those providing a liquid path around the internal in-line buffer, as well as other channels, which are not compressible, a priming system is desirable that does not require venting trapped air through the normal spray outlet channel by opening a pre-compression valve.